In one category of heating antenna reflectors, which may or may not be composite structures, elongated heating wires or strips are used. Unlike in the present invention, in which the heating fibers form part of the composite structure itself, the heating elements in these prior art references do not play any structural role, and in fact have a structural detriment. Examples of this category of prior art are: U.S. Pat. Nos. 2,679,003; 2,712,604; 2,864,927; and 3,146,449; French patent publication No. 2,426,343; and Japanese patent reference No. 57-65006. Compared with these references, the integral composite heater of the present invention offers the following advantages:
1. More reliable operation because it does not contain a single point of failure.
2. Avoidance of the delamination and debonding problems of the prior art, because there is only one coefficient of thermal expansion for the structure being heated and the heating means itself.
3. Can be tailored to provide either uniform heating or specified non-uniform heating.
4. Can readily be used on a contoured surface.
5. Utilizes inexpensive materials and techniques.
6. Immunity to puncture damage.
7. Employs voltages in safer ranges, because the resistance through the heating fibers is lower than in the wires of the prior art.
8. Greater immunity to EMP (electromagnetic pulses), because the heating means is homogeneous.
9. Maintenance-free operation.
10. Greater heating uniformity because of the continuous nature of the heating elements.
In a second approach to heating antenna reflectors, as exemplified by U.S. Pat. No. 4,259,671, hot air is used to heat the reflector.
U.S. Pat. No. 4,536,765 shows the use of a non-stick coating to prevent ice and snow build-up on an antenna reflector.
In a fourth approach of the prior art, a metallic spray, such as Spraymat (TM) manufactured by Lucas Aerospace, is sprayed on a surface to be heated. An electrical current is then passed through the spray to heat the surface. Compared with the present invention, this technique is very expensive and fragile.
Finally, U.S. Pat. No. 3,805,017 combines the techniques of heating wires and a thermally conductive but electrically nonconductive spray.